
import java.util.LinkedList;
import java.util.Queue;

class MyStack {
    private Queue<Integer> queue1 = new LinkedList<>();
    private Queue<Integer> queue2 = new LinkedList<>();
    public MyStack() {

    }
    
    public void push(int x) {
         if (!queue1.isEmpty()) {
             queue1.offer(x);
         } else if (!queue2.isEmpty()) {
             queue2.offer(x);
         } else {
             queue1.offer(x);
         }
    }
    
    public int pop() {
        if (empty()) {
            return -1;
        }
        if(!queue1.isEmpty()) {
            //出这个不为空的队列，出size-1
            int size = queue1.size();
            for(int i = 0;i < size-1;i++) {
                queue2.offer(queue1.poll());
            }
            return queue1.poll();
        } else {
            int size = queue2.size();
            for(int i = 0;i < size-1;i++) {
                queue2.offer(queue2.poll());
            }
            return queue2.poll();
        }
    }
    
    public int top() {
        if(empty()) {
            return -1;
        }

        if(!queue1.isEmpty()) {
            int size = queue1.size();
            int tmp = -1;
            for(int i = 0;i < size;i++) {
                tmp = queue1.poll();
                queue2.offer(tmp);
            }
            return tmp;
        } else {
            int size = queue2.size();
            int tmp = -1;
            for(int i = 0;i < size ;i++) {
                tmp = queue2.poll();
                queue1.offer(tmp);
            }
            return tmp;
        }
    }
    
    public boolean empty() {
        return queue1.isEmpty() && queue2.isEmpty();
    }
}